Conventional wireless sensor devices utilize batteries as the main power source for the sensing circuits and wireless transceiver. However, it is often desired to eliminate the battery from the system due to its limited capacity, size, cost (mainly maintenance cost), environmental impact, and operating limits. Ambient energy harvesting has found to be the most viable alternative source for low power, low data-rate wireless sensing applications, where the sensors monitor a physical quantity that changes slowly and needs to be transmitted infrequently. Depending on the application, a sensor node can harvest solar, thermal, vibrational, RF, or other forms of the ambient power.

This project involves design and implementation of a high performance Power Management IC (PMIC) for ambient energy harvesting. The core of the PMIC is a high-efficiency, ultra-low voltage, low-quiescent current, step-up converter which can harvest energy from one or more energy transducers and provide multiple supply rails to power the subsequent blocks and charge a temporary storage component. A power-aware analog front-end and low-power ADC are operated on a supply line from the PMIC. The sampling rate and resolution of the ADC are adaptively adjusted based on the available energy that is harvested and stored by the PMIC. Once the energy harvesting sensor platform is developed, the ambient energy transducer, micro-controller, and RF transceiver are added to create a complete energy harvesting wireless sensor node.

The first phase of the project (currently active) is the design of the power management IC. Since the available power from energy harvesting sources can range from few micro-watts to hundreds of milli-watts, design of a power converter covering the entire range leads to performance compromise. This problem can be mitigated by splitting the PMIC into two sub-converters: (1) a mW-converter aimed at harvesting energy from devices genrating milliwatts of power. A conventional switching-inductor DC-DC converter capable of harvesting energy from multiple sources is chosen primarily because of its high efficiency. (2) a uW-converter aimed at harvesting energy from chip-scale devices generating microwatts of power. A reconfigurable charge-pump architecture is chosen for the design of the uW-converter because it can be fully integrated on silicon and does not require additional off-chip component. The following block digram of the PMIC illustrates both sub-converters in more details.